Infrared emitting devices including semiconductor light emitting diodes and lasers operating in the midwave infrared region of the spectrum (defined herein as being a wavelength range of about 2 to 6 microns) have potential applications in many areas including fluoride-based optical-fiber communications, molecular spectroscopy, chemical and pollution sensing, process monitoring, and infrared laser radar and countermeasures.
In recent years, the art of III-V semiconductor light emitting devices has been advancing rapidly in the near-infrared region of the spectrum at wavelengths below about 1.5 microns. A lesser effort has been devoted to the development of III-V midwave infrared emitting devices, although such midwave emitters are expected to become increasingly important for the above applications.
Some prior art infrared emitters have been grown with III-V quaternary alloys for the active region and cladding layers surrounding the active region. In particular, U.S. Pat. No. 5,251,225 to Eglash et al discloses a quantum-well diode laser formed on a GaSb substrate with a quaternary active region of GaInAsSb quantum-wells separated by AlGaAsSb barrier layers, and quaternary AlGaAsSb cladding layers having a higher aluminum content than the barrier layers.
A disadvantage of using quaternary alloys for the formation of infrared emitting devices is that quaternary alloys are much more difficult to grow than ternary alloys.
Another disadvantage of the use the quaternary alloy GaInAsSb for the active region as in the Eglash et al patent is that this quaternary alloy is reported to have miscibility gaps that may limit the ability to fabricate infrared emitting devices at some midwave infrared wavelengths.
An advantage of the infrared emitting device and method of the present invention is that it is based on the growth of a ternary alloy active region, thereby simplifying epitaxial growth.
Another advantage of the present invention is that ternary alloys having layer compositions close to a III-V semiconductor substrate may be used, thereby providing for high-quality epitaxial growth.
Another advantage of the present invention is that the ternary alloys InAsSb and InGaAs have considerably lower binodal temperatures compared to the GaInAsSb quaternary alloys, making the ternary alloys suitable for the growth of homogeneous layer compositions at relatively low temperatures without phase segregation.
A further advantage of the present invention is that an active region of the infrared emitting device may be in the form of a strained-layer superlattice having a plurality of compressively-strained InAsSb quantum-well layers sandwiched between barrier layers formed of a semiconductor alloy having a smaller lattice constant and a larger energy bandgap than the quantum-well layers.
Still another advantage of the present invention is that a layer thickness of the compressively-strained InAsSb quantum-well layers may be selected to provide an increased activation energy for an Auger recombination process, thereby reducing an effect of the Auger process.
These and other advantages of the infrared emitting device and method of the present invention will become evident to those skilled in the art.